The Periodic Table

Section 1

D

mitri Mendeleev: Russian chemist who discovered a pattern to

the elements in 1869.

A

rranged the elements by density, appearance, and melting point.

He then finally arranged them by atomic mass. This is when

the pattern appeared. He noticed that those with similar

properties occurred in a repeating pattern. The pattern was

periodic.

The Periodic TableChapter 11 – Section 1

Periodic: describes something that occurs or repeats at regular intervals. Ex. days of the week.

Mendeleev even left blanks for undiscovered elements. He even made predictions for missing elements. Pg. 285. Some still did not fit. He hypothesized that the atomic mass was incorrect.

Henry Moseley in 1914 determined the number of protons---the atomic number.

Section 1

Periodic law: the law that states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements. The periodic table follows the periodic law.

Section 1

Three classifications of elements. It changes with the number of electrons in the outer energy level

• Metals: most elements. Metals are found on the left side of the zigzag line. Have few electrons in their outer shell. Most are solid at room temperature. Tend to be shiny, ductile, good conductors of electrical and thermal heat, malleable

• Nonmetals: Found to the right of the zigzag line. Almost have a complete set of electrons in outer level. Group 18 has a complete set of electrons. More than half of nonmetals are gases at room temperature. Mostly, the opposite properties of metals. Not ductile or malleable, not shiny, poor conductors of thermal energy and electrical current.

Section 1

Metalloids: Semiconductors. They border the zigzag line. More outer electrons than metals but less than nonmetals. Has properties of metals and nonmetals.

Section 1

Each square on periodic table includes an element’s name, chemical symbol, atomic number, and atomic mass. If two letters the first is always capitalized and the second is lower case.

Period: in chemistry, a horizontal row of elements in the periodic table. From left to right. The chemical properties change gradually as you move across the table---ex. conductivity and reactivity.

Group: a vertical column of elements in the periodic table; elements in a group share chemical properties. Top to bottom. Elements in the same group often have similar chemical and physical properties. Often called families.

The Periodic TableChapter 11 – Section 2

Alkali metal: one of the elements of Group 1 of the periodic table (lithium, sodium, potassium, rubidium, cesium, and francium). Very reactive. Often soft, color of silver, shiny, and low density. Most reactive of the metals. 1 electron in outer shell

Alkaline-earth metal: one of the elements of Group 2 of the periodic table (beryllium, magnesium, calcium, strontium, barium, and radium). Two electrons in outer shell. They are very reactive but less reactive than Alkali metals. Higher density than alkali metals. Often found in the earth.

Alkali, Alkaline-earth metals, and halogens are never found free in nature. They are always in a compound.

Section 2

Transition metals: 1 or 2 electrons in outer shell. Less reactive than alkaline earth metals. Shiny, good conductors of thermal and electrical energy. Higher densities and melting points than elements in groups 1 or 2.

Lanthanides: Starts with lanthanum

Actinides: Starts with actinium

• They appear at the bottom to keep the table from being too wide.

Section 2

G

roup 13: Boron Group: Aluminum, the most abundant metal in

the earth’s crust. Has three electrons in their outer shell.

They are reactive and solids at room temperature.

G

roup 14: Carbon Group: One nonmetal, two metalloids, and

three metals. Four electrons in their outer shell. Carbon forms

a wide variety of compounds. Si and Ge are the metalloids.

Section 2

G

roup 15: Nitrogen Group: two nonmetals, two metalloids, and two metals. Five

electrons in their outer shell. Nitrogen composes 80% of our atmosphere.

G

roup 16: Oxygen Group: three nonmetals, one metalloid, and one metal. Six

electrons in the outer shell.

G

roup 17: Halogens: nonmetals, seven electrons in their outer shell. Very

reactive---wants to fill outer shell. Poor conductors of electrical current,

violent reactions with alkali metals to form salts. Never in uncombined form in

nature. (fluorine, chlorine, bromine, iodine, and astatine). All are nonmetals.

The Periodic TableChapter 11 – Section 2

N

oble gas: one of the elements of Group 18 of the periodic table

(helium, neon, argon, krypton, xenon, and radon); noble gases are un-

reactive. Nonmetals, eight electrons in outer shell except helium which

has two, unreactive, colorless, and odorless.

H

ydrogen: one electron in outer shell. Reactive, colorless, odorless gas

at room temperature, low density. Does not match the properties of

any single group so hydrogen is has its own group. It is above group

one because the metals in group one also have one outer electron.

Physical properties are more like nonmetals.